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Full text of "Treatise On Applied Analytical Chemistry(Vol-1)"

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French degrees.
	German degrees.
	English degrees.

I
	0-56
	0-70

1-79
	I
	1-25

1-43
	0-80
	I

POTABLE WATERS                                     5

of CaO per 100 litres of water, so that a water with 10 German or Clark
degrees will contain 10 grams per 100 litres of calcium or magnesium oxide
combined with carbonic, sulphuric, hydrochloric and nitric acids.1

If the number of c.c. of soap solution used does not occur in the table,
the corresponding degree of hardness is determined by interpolation.

Examples. 100 c.c. of a water required 39-8 c.c. of soap solution ; the nearest
number in the table is 40-1, corresponding with 10-5 degrees of hardness. Hence

40-1 — 39-8       =0-3
0-3 X   0-294   — 00882
and 10-5 —   0-0882 = 10-4118,
the degree of hardness being therefore 10-41.

Another water required 32-0 c.c. of soap solution ;
32-0 — 31-6       = 0-4
0-4 X   0-277   = 0-1108
and   8-0 -f-   0-1108 = 8-n

The permanent and also the temporary hardness are determined as
under (a).

The relations between French, English, and German degrees of hardness
are shown in the following table :

I   French degree
i German degree    .
i English degree

3. Alkalinity.—By the alkalinity of a water is meant the quantity of
calcium and magnesium carbonates and, where present, alkali carbonates
present in the water ; it is, therefore, related to the hardness.

Its determination, proposed by Wartha and Pfeiffer, may replace that
of the hardness, especially when it is desired to compare rapidly a number
of samples of water or to detect any slight variations which a given water
may undergo.

According to Gigli, the alkalinity of a water (total, permanent and
temporary) is easily determined as follows :z

100 c.c. of the water are titrated with N/20-hydrochloric acid in presence
of 2 drops of o-i % aqueous methyl orange solution. The result is expressed
as CaC03 per litre (i c.c. = 0-0025 gram of CaC03) and represents the total
alkalinity, that is, the alkali and alkaline earth carbonates.

Another 100 c.c. of the water is boiled for 12 minutes in a reflux appara-
tus, allowed to cool and filtered, the filter being washed with a little boiled,
distilled water and the whole of the filtrate titrated as before. From the
volume of N/2o-acid used in this second determination it is necessary to
subtract that required to neutralise the alkalinity transferred to the water
from the glass during boiling, this being determined by a blank test with
distilled water. Good Jena glass produces in 100 c.c. of water, after 12
minutes' boiling, an alkalinity corresponding with about 0-25 c.c. of N/20-
HC1.

1  English degrees represent grains of CaO per gallon of water, that is grams of CaO
per 70 litres.

2  L'industna chimica, mineraria e metallurgica, 1914, p. 289.es :